Large nonlinear refraction in pulsed laser deposited BCZT thin films on quartz substrates

Abstract

Optical thin films based on ferroelectric materials are forerunners for novel optoelectronic and photonic applications due to their large inherent coupling between optical and electrical properties. We report here on the thickness dependence of linear and nonlinear optical properties of polycrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) thin films fabricated on quartz substrates by the pulsed laser deposition technique. In order to probe the linear optical properties of BCZT thin films, we have obtained optical transmission spectra from which the optical parameters like the refractive index and extinction coefficient were deduced using the Swanepoel method. Using the Sellemier relation, we have estimated the oscillator parameters like oscillator strength and oscillator energy from the refractive index dispersion data, which are indicative of the efficiency of the electro-optic coupling process. Further, the third-order optical nonlinearity of these thin films was measured by a closed-aperture Z-scan technique with a low-power, continuous-wave He–Ne laser as the excitation source. These films exhibited high optical nonlinearity, and the nonlinear refractive index was determined to be ∼5×10−7 m2/W. The enhanced nonlinear refraction in BCZT thin films at the low power regime could be attributed to both photothermal and photorefractive origin with a plausible larger contribution from the latter. Such a large nonlinear optical response exhibited at low optical powers in BCZT thin films is very promising technologically, as it may find applications in a number of photonic devices such as optical interconnects, optical processors, optical memories, and waveguide modulators.